Magister Scientiae Dentium - MSc(Dent) / Over the last few decades, and throughout the world, there would seem to have been an increase in the number and severity of infections affecting the maxillofacial region. In the South African setting this seems to be especially evident in the state health system. Maxillofacial infection of odontogenic origin is largely preventable. If treated appropriately and early in the pathological process, the progression of the disease process is generally prevented and complications avoided. Management of maxillofacial infections once established has serious implications for patients and an already stressed health system. The reasons for this perceived increase in infections are likely multifactorial and it is hoped that this study may aid in understanding factors contributing to this burden.

Voice over Internet Protocol (VoIP), also called IP telephony is rapidly becoming a familiar term and as a technology it is invading the enterprise, private usage, and educational and government organizations. Exploiting advanced voice coding & compression techniques and bandwidth sharing over packet switched networks, VoIP can dramatically improve bandwidth efficiency. Moreover enhanced security features, mobility support, and cost reduction features of VoIP are making it a popular choice for personal communication. Due to its rapid growth in popularity VoIP is rapidly becoming the next generation phone system. Lawful interception is a mean of monitoring private communication of users that are suspected of criminal activities or to be a threat to national security. However, government regulatory bodies and law enforcement agencies are becoming conscious of the difficulty of lawful interception of public communication due to the mobilitysupport and advanced security features implemented in some implementations of VoIP technology. There has been continuous pressure from the government upon the operators and vendors to find a solution that would make lawful interception feasible and successful. Key escrow was proposed as a solution by the U. S. National Security Agency. In key escrow the key(s) for a session are entrusted to a trusted third party and upon proper authorization law enforcement agencies can receive the session key(s) from this trusted third party However, key escrow adds some security vulnerabilities and potential risks as an unethical employee of the key escrow agent (or a law enforcement agency that has received the session key(s)) can misuse the key(s) to forge content of a communication session -- as he or she possesses the same key(s) as the user used for this session. This thesis addresses the issue of forged session content, by proposing, implementing, and evaluating a cryptographic model which allows key escrow session content. The implementation utilizes an existing implementation of a Session Initiation Protocol (SIP) user agent ‘minisip’ developed at KTH. The performance evaluation results suggest that the proposed model can support key escrow while protecting the user communication from being forged with the cost of minimal computational resource and negligible overhead. without the possibility of undetectable fabrication of  session content. The implementation utilizes an existing implementation of a Session Initiation Protocol (SIP) user agent ‘minisip’ developed at KTH. The performance evaluation results suggest that the proposed model can support key escrow while protecting the user communication from being forged with the cost of minimal computational resource and negligible overhead.

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Inspirés par les propriétés optiques des yeux composés de la mouche et par l’observation de micromouvements périodiques de sa rétine, différents capteurs visuels ont montré qu’il était possible de localiser un contraste très précisément. Ce fut les premières démonstrations d’hyperacuité visuelle de l’œil de la mouche.Dans cette thèse, un œil composé artificiel, doté d'un large champ de vision, est utilisé. Grâce à un nouvel algorithme de fusion des données visuelles, cet œil peut mesurer le déplacement d’un robot et lui permettre de se stabiliser au-dessus d’un environnement texturé. Localiser un contraste de manière linéaire sur l'ensemble du champ visuel demeure toutefois difficile. Un deuxième algorithme permet d’améliorer la localisation d’une barre grâce à un étalonnage, mais montre une certaine dépendance aux variations de contraste et de luminosité ambiante.Afin d'éviter ce processus d’étalonnage, un troisième algorithme qui s’appuie sur les travaux d'Heiligenberg et Baldi, a été proposé pour localiser deux contrastes. Ces auteurs ont montré que la somme pondérée de plusieurs capteurs ayant un champ récepteur gaussien pouvait fournir une estimation linéaire de la position d'un stimulus. Nous avons, pour la première fois, appliqué une variante de ce principe à un œil composé artificiel. Cet œil, une fois monté sur un robot permet de suivre une cible à une distance constante.Finalement, un œil composé artificiel dont la résolution intrinsèque est faible, peut être doté d’une hyperacuité visuelle et permettre de suivre une cible avec précision. Ces travaux ont ainsi conduit à proposer des stratégies bio-inspirées pour la localisation et la poursuite de cible. / Inspired by the optical properties of the fly compound eyes and the observation of its retinal periodic micro-movements, several visual sensors established that the localization of a contrast can be made very precisely. It was the first demonstration of the visual hyperacuity of the fly compound eye.In this thesis, an artificial compound eye with a wide field of view was used. Thanks to a novel algorithm fusing the visual signals, the sensor embedded onboard an aerial robot measures its displacement and enables the robot to hover above a textured environment.The localization of a contrast precisely over the whole field of view is still difficult. A second algorithm improved the localization of a bar thanks to a calibration. But it has a dependency to the contrast and the illuminance variations.In order to avoid a calibration process, a third algorithm was proposed to localize two contrasts. It is based on the work of Heiligenberg and Baldi, which showed that an array of Gaussian receptive field can provide a linear estimation of a stimulus position. For the first time, we applied a modified version of their estimation to an artificial compound eye. This sensor mounted on a rover allows following a target precisely at a constant distance.Finally, an artificial compound eye with a coarse spatial resolution can be endowed with hyperacuity and enables a robot to follow a target with precision. A step forward has been made toward bio-inspired target localization and pursuit.

L'objectif de cette thèse est d'étudier le comportement de traversée d'intersection en conduite automobile sous l'angle des actions visuellement guidées. Dans l'introduction, nous montrons que les principales études portant sur la traversée d'intersection se sont focalisées sur les processus de jugement perceptif ; or nous montrons que la compréhension de cette activité pourrait être affinée en utilisant les concepts de la théorie de la perception directe et ceux issus du contrôle continu. Notre revue de questions nous conduit à rapprocher la tâche de traversée d'intersection à l'intérieur d'un créneau libre du trafic à celle d'interception de cible se déplaçant horizontalement. Or, dans le cadre des tâches d'interception, il a été démontré que la stratégie d'angle de relèvement constant (i.e., Constant Bearing Angle, CBA) a un fort pouvoir explicatif vis-à-vis des données expérimentales. Nous avons donc tiré partie des outils de simulation automobile pour tester la plausibilité de l'utilisation d'une telle stratégie par les conducteurs. Dans le premier chapitre expérimental, nous montrons qu'il est légitime d'étudier le couplage perception-action dans ce type de tâche et que les conducteurs adoptent des régulations comportementales proches de celles observées dans une tâche d'interception de mobile. Le second chapitre expérimental nous permet de mettre en évidence l'utilisation conjointe par les conducteurs d'informations relatives au créneau du trafic (supports globaux) et aux véhicules (supports locaux). / This Ph.D. project aims at studying drivers' road crossing behaviour under the perspective of visually guided actions. In the introduction, we present that former studies related to road crossing behaviour mainly focused on perceptual judgement processes. However, we demonstrate that this kind of task would be better understood with theories from the ecological approach of perception and motor control studies. Our literature review lead us to make a bridge between the task of crossing a road inside a free moving traffic gap and the task of intercepting an horizontally moving target. In this regard, it has been demonstrated that the Constant Bearing Angle strategy (CBA) has a high explanatory power in respect to experimental data. We used driving simulation tools in order to assess the hypothesis of the use of bearing angle based strategy by drivers. In the first experimental chapter, we show that studying perceptual-motor coupling in this task is relevant and that observed behaviour is close to taht observed in horizontally moving target interception tasks. The second experimental chapter demonstrates that drivers' behaviour relies both on visual information related to the moving gap (global contribution) and that related to the independent vehicles (local contributions). In the last experimental chapter, we evidenced that drivers' behaviour does not exclusively rely on the changes of the bearing angle but also on traffic vehicles' optical expansion. We conclude on how our results shed new light on former results obtained with perceptual-judgements based methodology.

Dans une tâche virtuelle d'interception, nous nous sommes intéressés à la façon dont deux individus, pouvant déplacer chacun une raquette le long d'un axe d'interception commun, coordonnaient leurs actions dans le but d'intercepter une balle qui s'approchait. En tant que contact entre les raquettes rendrait interception impossible, la tâche de double-pong demandait aux participants de décider à chaque essai qui allait être celui à réaliser l'interception. Sans possibilités pour communication orale, seules les informations visuelles sur l’écran pouvaient être utilisées lors processus décisionnel. A travers trois expériences, en manipulant les positions initiales des raquettes et les différences individuelles de niveaux au sein des équipes, nous avons examiné comment ces équipes organisaient leur comportement d'interception. Les résultats ont révélé que toutes les équipes établissaient spontanément une division du travail caractérisée par des domaines d'interception individuels séparés par des frontières floues. Bien que les positions des limites puissent varier d'une équipe à l'autre, celles-ci ont été systématiquement affectées par les positions initiales des raquettes. Les différences de niveaux ne semblaient pas avoir un tel effet. Une définition basée sur l'action de l'opportunité selon laquelle, à chaque instant, chaque joueur se déplace vers la future position d'interception, a permis de prédire qui finirait par intercepter la balle. Dans l'ensemble, nos études suggèrent que la prise de décision de qui va intercepter la balle émerge d'un couplage informationnel entre les membres de l'équipe, considérant que la division de l'espace est un résultat émergent. / We studied the way two individuals coordinate their actions in order to intercept an approaching ball by moving individually-controlled paddles along a common interception-axis in a video game-like doubles interception task. With contact between paddles leading to their immediate disintegration, the doubles-pong task required team members to decide on each trial who would be the one to actualize the interception. Because overt communication was precluded, these decisions were informed exclusively by vision of the on-screen movements of paddles and ball. In three experiments, manipulating initial conditions (i.e., initial paddle positions) and individual skill differences within teams, we examined how teams organized their joint interception behavior. Results revealed that all teams spontaneously demonstrated a division of labor, characterized by individual interception domains separated by fuzzy (i.e., overlapping) boundaries. While boundary locations could vary over teams within a given experimental condition, they were nevertheless systematically affected for each team by initial paddle positions. Skill differences between individual team members did not appear to have such an effect. An action-based definition of the (time-evolving) expediency with which each player moved towards the future interception position allowed predicting which of the two players would end up intercepting the ball and which would abandon the interception attempt. Overall, our studies suggest that the decision of who will intercept the ball emerges from an informational coupling between team members, with the division of space being an emergent result.

In this thesis, the problem of intercepting highly manoeuvrable threats using seeker-less interceptors that operate in the command guidance mode, is addressed. These systems are more prone to estimation errors than standard seeker-based systems. Several non-linear and optimal estimation and guidance concepts are presented in this thesis for interception of randomly maneuvering targets by seeker-less interceptors. The key contributions of the thesis can be broadly categorized into six groups, namely (i) an optimal selection of bank of lters in interactive multiple model (IMM) scheme to cater to various maneuvers that are expected during the end-game, (ii) an innovative algorithm to reduce chattering phenomenon and formulate effective guidance algorithm based on 'differential game guidance law' (modi ed DGL), (iii) IMM/DGL and IMM/modified DGL based integrated estimation/guidance (IEG) strategy, (iv) sensitivity and robustness analysis of Kalman lters and ne tuning of lters in filter bank using innovation covariance, (v) Performance of tuned IMM/PN, tuned IMM/DGL and tuned IMM/modi ed DGL against various target maneuvers, (vi) Performance comparison with realistic missile model. An innovative generalized state estimation formulation has been proposed in this the-sis for accurately estimating the states of incoming high speed randomly maneuvering targets. The IMM scheme and an optimal selection of lters, to cater to various maneu-vers that are expected during the end-game, is described in detail. The key advantage of this formulation is that it is generic and can capture evasive target maneuver as well as straight moving targets in a uni ed framework without any change of target model and tuning parameters. In this thesis, a game optimal guidance law is described in detail for 2D and 3D engagements. The performance of the differential game based guidance law (DGL) is compared with conventional Proportional Navigation (PN) guidance law, especially for 3D interception scenarios. An innovative chatter removal algorithm is introduced by modifying the differential game based guidance law (modified DGL). In this algorithm, chattering is reduced to the maximum extent possible by introducing a boundary layer around the switching surface and using a continuous control within the boundary layer. The thesis presents performance of the modified DGL algorithm against PN and DGL, through a comparison of miss distances and achieved accelerations. Simulation results are also presented for varying fiight path angle errors. Apart from the guidance logic, two novel ideas have been presented following the evolving "integrated estimation and guidance" philosophy. In the rst approach, an in-tegrated estimation/guidance (IEG) algorithm that integrates IMM estimator with DGL law (IMM/DGL), is proposed for seeker-less interception. In this interception scenario, the target performs an evasive bang-bang maneuver, while the sensor has noisy measure-ments and the interceptor is subject to an acceleration bound. The guidance parameters (i.e., the lateral acceleration commands) are computed with the help of zero e ort miss distance. The thesis presents the performance of the IEG algorithm against combined IMM with PN (IMM/PN), through a comparison of miss distances. In the second ap-proach, a novel modi ed IEG algorithm composed of IMM estimator and modi ed DGL guidance law is introduced to eliminate the chattering phenomenon. Results from both of these integrated approaches are quite promising. Monte Carlo simulation results re-veal that modi ed IEG algorithm achieves better homing performance, even if the target maneuver model is unknown to the estimator. These results and their analysis o er an insight to the interception process and the proposed algorithms. The selection of lter tuning parameters puts forward a major challenge for scien-tists and engineers. Two recently developed metrics, based on innovation covariance, are incorporated for determining the filter tuning parameters. For predicting the proper combination of the lter tuning parameters, the metrics are evaluated for a 3D interception problem. A detailed sensitivity and robustness analysis is carried out for each type of Kalman lters. Optimal and tuned Kalman lters are selected in the IMM con guration to cater to various maneuvers that are expected during the end-game. In the interception scenario examined in this thesis, the target performs various types of maneuvers, while the sensor has noisy measurements and the interceptor is subject to acceleration bound. The tuned IMM serves as a basis for synthesis of e cient lters for tracking maneuvering targets and reducing estimation errors. A numerical study is provided which demonstrates the performance and viability of tuned IMM/modi ed DGL based modi ed IEG strategy. In this thesis, comparison is also performed between tuned IMM/PN, tuned IMM/DGL and tuned IMM/modi ed DGL in integrated estimation/guidance scheme. The results are illustrated by an extensive Monte Carlo simulation study in the presence of estimation errors. Simulation results are also presented for end game maneuvers and varying light path angle errors . Numerical simulations to study the aerodynamic e ects on integrated estimation/ guidance structure and its e ect on performance of guidance laws are presented. A detailed comparison is also performed between tuned IMM/PN, tuned IMM/DGL and tuned IMM/modi ed DGL in integrated estimation/guidance scheme with realistically modelled missile against various target maneuvers. Though the time taken to intercept is higher when a realistic model is considered, the integrated estimation/guidance law still performs better. The miss distance is observed to be similar to the one obtained by considering simpli ed kinematic models.

Various unmanned missions deploy vehicles such as missiles, torpedoes, ground robots, and unmanned aerial vehicles. Guidance strategies for these vehicles aim to intercept a target point and satisfy additional objectives such as specifications on impact angle and interception time. Certain impact angles are crucial for a greater warhead effectiveness, and minimizing the interception time is important for vehicles with limited endurance time and for reducing the probability of detection. This thesis considers the time-optimal impact angle constrained guidance problem for interception of moving targets. In the first part of the thesis, a Dubins paths–based guidance methodology for minimum-time lateral interception of a moving and non-maneuvering target is designed. The existence and the time-optimality of the paths are established for impact angle constrained interception of moving targets. The capture regions are analyzed and a classification of the initial geometries is developed for deducing the time-optimal path type. The corresponding guidance command for optimal interception can be generated from the information of initial engagement geometry and target’s speed. In the next part of the thesis, the concept of equivalent virtual target is introduced to address the problem of impact along a general direction. An algorithm is developed to obtain the optimal interception point for generalized interception scenarios. A proof of convergence is presented for the proposed algorithm. Achieving different impact angles, the interceptor often takes sharp turns. Following such curved trajectories, the interceptor may fail to keep the target inside the seeker field-of-view. In the next part of the thesis, the field-of-view characteristics of the proposed optimal guidance strategies are analyzed. Closed-form expressions are derived for the interceptor’s look-angle to the target. Satisfying field-of-view condition at endpoints of the path segments that constitute the optimal path is proven to guarantee target motion inside the field-of-view throughout the engagement. The stationary target case is also analyzed as a specific scenario. The last part of the thesis presents a method to extend the proposed guidance strategies to maneuvering target scenarios.

L’objectif de cette thèse est de comprendre le comportement cinématique d’interception latérale manuelle et locomotrice. Dans l’introduction nous montrons que l’étude du mouvement d’interception peut être engagée avec les concepts de la perception directe et du couplage perception-action. De nombreux travaux ont montré qu’une stratégie prospective serait mise en oeuvre pour intercepter un mobile mais un débat existe quant à la double question (i) quelle information est utilisée pour réguler le mouvement ? (ii) comment est utilisée cette information ? Pour répondre nous avons utilisé la réalité virtuelle. Dans le premier chapitre expérimental nous montrons que les variables environnementales qui ont émergées de la littérature ne peuvent expliquer seules les régulations du mouvement d’interception. Dans le deuxième chapitre expérimental nous proposons qu’une variable d’ordre intermédiaire plutôt qu’entier pourrait guider le mouvement. Enfin dans le troisième chapitre expérimental nous apportons des éléments de preuve en faveur du concept d’information d’ordre fractionnaire qui augmenterait au cours de l’action. Nous développons dans ces deux dernières études deux modèles dynamiques qui nous permettent de simuler de façon satisfaisante le comportement cinématique d’interception latérale pour une situation donnée. Plus généralement, nous suggérons, quant à l’ensemble des modèles dynamiques formalisant les interactions perception-action, que cette proposition conceptuelle pourrait permettre de plus larges avancées encore si l’on considérait l’éventuelle sensibilité des différents organismes vivants aux informations d’ordre intermédiaire plutôt que nécessairement entier. / The goal of the present thesis was to understand the operative perception-action relations underlying the kinematic patterns of movement observed in manual and locomotor lateral interception. The introduction sets the stage for this endeavor, calling upon the theoretical concepts of direct perception and information-movement coupling, understood as a particular form of the online control of movement. Whereas a large body of work has demonstrated that interception is based on a prospective control strategy, debate persists as to the double question of (i) what information is that used to regulate the movement and (ii) how this information is used in the regulation of movement. To address these questions our general methodology was based on interception tasks presented in virtual reality settings. In the first experimental chapter we demonstrate that neither of the two variables proposed in the literature could by themselves explain the kinematic patterns observed. Integrating an modeling approach based on attractor dynamics, the second experimental chapter provides first evidence for reliance on a variable of intermediate rather than integer order. In the third experimental chapter we take our modeling approach one step further and demonstrate that reliance on information of a trajectory-dependent fractional order allows capturing the qualitative and quantitative aspects of the interception behavior observed. In the final chapter we discuss the suggested potential of opening up the information space to non-integer orders for the understanding of perception-action relations.

Cette étude propose d’analyser l’influence de l’architecture du palmier à huile sur sa capacité à intercepter la lumière, en se basant sur des reconstructions 3D de palmiers et en établissant un bilan radiatif sur ses structures végétales reconstruites in silico. Le premier objectif de l’étude était de caractériser et modéliser la variabilité génétique de l’architecture du palmier à huile et de son interception lumineuse. Dans un deuxième objectif l’amélioration potentielle de l’interception de la lumière et de l’assimilation carbonée a été évaluée en modifiant les traits morphologiques et géométriques des feuilles et des idéotypes architecturaux de palmiers à huile ont été proposés.Des relations allométriques ont été utilisées pour modéliser les traits architecturaux en fonction de gradients ontogénétique et de topologie des feuilles dans la couronne. La méthode permet de reconstruire des palmiers à huile virtuels à différents âges au cours du développement. De plus, l’approche allométrique a été couplée à des modèles à effets mixtes pour intégrer au travers de paramètres la variabilité entre et au sein des cinq progénies. Le modèle permet ainsi de simuler les spécificités architecturales des cinq progenies en incluant les variabilités entre individus observés. Le modèle architectural, paramétré pour les différentes progénies, a ensuite été implémenté dans AMAPstudio pour générer des maquettes 3D de palmiers et ainsi estimer leur interception lumineuse, de l’individu à la parcelle entière.Les résultats de ces analyses ont révélé des différences significatives entre et au sein des progenies, dans la géométrie des feuilles (longueur du pétiole, densité de folioles sur le rachis, et courbure du rachis) et dans la morphologie des folioles (gradients de longueurs et largeurs le long du rachis). La comparaison virtuelle des différentes progénies ont aussi montré des efficacités distinctes de l’interception lumineuse.Des analyses de sensibilité ont ensuite été réalisées pour identifier les traits architecturaux influençant l’interception lumineuse et l’assimilation potentielle à différents âges de la plante. Les paramètres les plus sensibles au cours du développement furent ceux reliés à la surface totale foliaire (longueur des rachis, nombre de folioles, morphologie des folioles), mais les attributs géométriques plus fins de la feuille ont montré un effet croissant avec la fermeture de la canopée. Sur un couvert adulte, l’optimum en assimilation carbonée est atteint pour des indices de surfaces foliaires (LAI) entre 3,2 et 5,5 m2.m−2, avec des feuilles érigées, de courts pétioles et rachis et un nombre important de folioles sur le rachis. Quatre idéotypes architecturaux pour l’assimilation carbonée ont été proposés et présentent des combinaisons spécifiques de traits géométriques, limitant l’ombrage mutuel des plantes et optimisant la distribution de la lumière dans la couronne.En conclusion, le modèle 3D de palmiers à huile, dans sa conception et son application, a permis de détecter les traits architecturaux génétiquement déterminés et influençant l’interception lumineuse. Ainsi, le nombre limité de traits dégagés par l’analyse de sensibilité ainsi que les combinaisons de traits révélées au travers des idéotypes pourraient être pris en compte dans de futurs programmes de sélection. En perspective, des travaux dédiés à intégrer dans ce modèle d’autres processus physiologiques, tels que la régulation de la conductance stomatique et le partitionnement du carbone dans la plante, sont à envisager. Ce nouvel FSPM pourrait alors être utilisé pour tester différents scénarii, comme par exemple dans un contexte de changement climatique avec de faibles radiations et des périodes de sécheresse fréquentes. De même, ce modèle pourrait être utilisé pour étudier différentes configurations de plantation et des systèmes de cultures intercalaires, et ainsi proposer de nouveaux idéotypes multicritères / In this study we proposed to investigate the influence of oil palm architecture on the capacity of the plant to intercept light, by using 3D reconstructions and model-assisted evaluation of radiation-use efficiency. The first objective of this study was to analyse and model oil palm architecture and light interception taking into account genetic variability. A second objective was to explore the potential improvements in light capture and carbon assimilation by manipulating oil palm leaf traits and propose architectural ideotypes.Allometric relationships were applied to model these traits according to ontogenetic gradients and leaf position within the crown. The methodology allowed reconstructing virtual oil palms at different stages over plant development. Additionally, the allometric-based approach was coupled to mixed-effect models in order to integrate inter and intra progeny variability through progeny-specific parameters. The model thus allowed simulating the specificity of plant architecture for a given progeny while including observed inter-individual variability. The architectural model, parameterized for the different progenies, was then implemented in AMAPstudio to generate 3D mock-ups and estimate light interception efficiency, from individual to stand scales.Significant differences in leaf geometry (petiole length, density of leaflets and rachis curvature) and leaflets morphology (gradients of leaflets length and width) were detected between and within progenies, and were accurately simulated by the modelling approach. Besides, light interception estimated from the validated 3D mock-ups showed significant variations among the five progenies.Sensitivity analyses were then performed on a subset of architectural parameters to identify the architectural traits impacting on light interception efficiency and potential carbon assimilation over plant development. The most sensitive parameters over plant development were those related to leaf area (rachis length, number of leaflets, leaflets morphology), but fine attribute related to leaf geometry showed increasing influence when canopy got closed. In adult stand, optimized carbon assimilation was estimated on plants presenting a leaf area index (LAI) between 3.2 and 5.5 m2.m−2, with erected leaves, short rachis and petiole and high number of leaflet on rachis. Four architectural ideotypes for carbon assimilation were proposed based on specific combinations of organs geometry, limiting mutual shading and optimizing light distribution within plant crown.In conclusion, this study highlighted how a functional-structural plant model (FSPM) can be used to virtually explore plant biology. In our case of study, the 3D model of oil palm, in its conception and its application, permitted to detect the architectural traits genetically determined and influencing light interception. The limited number of traits revealed in the sensitivity analysis and the combination of traits proposed through ideotypes could guide further breeding programs. Forthcoming work will be dedicated to integrate in the modeling approach other physiological processes such as stomatal conductance and carbon partitioning. The improved FSPM could then be used to test different scenarios, for instance in climate change context with low radiations or frequent drought events. Similarly, the model could be used to investigate different planting patterns and intercropping systems, and proposed new multi-criteria ideotypes of oil palm.